The use of a hand operated pointing device with a computer and its display has become almost universal. One form of the various types of pointing devices is the conventional (mechanical) mouse, used in conjunction with a cooperating mouse pad. Mechanical mice typically include a rubber-surfaced steel ball that rolls over the mouse pad as the mouse is moved. Interior to the mouse are rollers, or wheels, that contact the ball at its equator and convert its rotation into electrical signals representing orthogonal components of mouse motion. These electrical signals are coupled to a computer, where software responds to the signals to change by a ΔX and a ΔY the displayed position of a pointer (cursor) in accordance with movement of the mouse.
In addition to mechanical types of pointing devices, such as a conventional mechanical mouse, optical pointing devices have also been developed. In one form of an optical pointing device, rather than using a moving mechanical element like a ball, relative movement between an imaging surface, such as a finger or a desktop, and photo detectors within the optical pointing device, is optically sensed and converted into movement information.
In some optical pointing devices, motion is determined from two-dimensional (2-D) cross-correlations of image sequences. The two-dimensional nature of the data results in significant computational complexity, and a large memory is typically used to store the image arrays that are used for correlation. The two-dimensional nature of the data constrains the maximum frame rate at which images can be acquired and processed. As a result, the pixel pitch of the image sensor is lower bounded to enable navigation up to some maximum velocity.